The CBFB-MYH11 fusion oncogene is frequently found in acute myeloid leukemia (AML). Our long term goal is to elucidate the molecular mechanisms that determine CBFB-MYH11-mediated leukemia progression in order to provide targets for the design of improved therapies. Our general hypothesis is that CBFB-MYH11 expression reduces hematopoietic stem cell differentiation and proliferation, and that cooperating mutations affect programs associated with proliferation, and survival. We have determined that Cbfb-MYH11 induces AML in cooperation with other mutations. We have created a conditional mouse model to show that expression of the fusion gene reduced the differentiation and proliferation ability of hematopoietic progenitors and created leukemia precursors in the myeloid compartment. Furthermore, we have identified cooperating genes, such as the transcription factors Plag1 and PlagL2 and the microRNA cluster miR17-92, and shown that constitutive expression of the transcription factor PlagL2 expanded myeloid progenitors and induced AML in the presence of Cbfb-MYH11. Based on these findings, the specific aims of this proposal are to: (1) determine PlagL2 role in proliferation and self-renewal of hematopoietic progenitors. We will use competitive repopulation and serial transplantation assays to assess the effect of (a) PlagL2-loss, and (b) constitutive PlagL2 expression, in long term-hematopoietic stem cells. (2) define the mechanism of PlagL2 function in leukemia progression. Preliminary experiments indicated that PlagL2 induces Mpl/Jak2 and TGF-beta signaling. We will combine in vivo and biochemical assays to determine the molecular mechanism of PlagL2 function in the (a) Mpl/Jak2 and (b) TGF-beta pathways. In addition, we will test whether Plag expression is necessary for maintenance of leukemia. (3) determine the role of micro-RNAs in CBF-SMMHC -mediated acute myeloid leukemia. Preliminary genetic evidence indicated that micro-RNAs can cooperate with Cbfb-MYH11 in leukemia progression. We will use in vivo assays to identify the mechanism of microRNA transformation. [unreadable] [unreadable] [unreadable]